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For more than 25 years, many scientists subscribed to the idea that tiny marine plants played a starring role in regulating climate change. A new study, published today in the journal Nature, indicates that the phytoplankton’s part is more of a walk-on.

Researchers in the fields of biological oceanography, atmospheric chemistry, and climate science have long searched for evidence of biological regulation of climate caused by marine emissions.

“For many years, we thought that chemical emissions from phytoplankton was the major player in cloud drop formation in the marine atmosphere and, as such, had a strong influence on the amount of solar radiation reflected back into space,” said Timothy Bates, a supervisory research chemist at NOAA’s Pacific Marine Environmental Laboratory in Seattle, Wash. and one of the co-authors of the paper.

“But after looking at two decades of observations and computer simulations, we concluded that  the role of phytoplankton emissions is much smaller than originally thought, and therefore, does not have a significant part in counteracting climate change,” he said.

The CLAW hypotheses, named after the four authors of the original paper (Charlson, Lovelock, Andreae, and Warren), suggested that the emission of the sulfur compound dimethyl sulfide resulted in small atmospheric particles that acted as the nuclei that took up water to create cloud droplets. An increase in dimethyl sulfide would result in an increase in the number of small cloud droplets and cloud reflectivity or albedo. The end result would be a biologically regulated climate feedback loop that could lessen the impacts of climate change.

“Putting this hypothesis to rest doesn’t rule out a link between ocean emissions and climate, however,” said Patricia Quinn, a PMEL research chemist and co-author of the study. “Sea spray made up of sea salt and a variety of organic compounds also provides a source of nuclei for cloud droplets to the marine atmosphere. Because sea spray organics are emitted directly into the atmosphere as particles, there is the potential for a link between ocean biology, cloud drop formation, and cloud albedo.”

Quinn and Bates note that by sending CLAW offstage, the research community can now address the complexity of multiple sources of cloud droplet nuclei to the marine atmosphere and potential impacts on climate.
The paper, titled “The case against climate regulation via oceanic phytoplankton sulfur emissions,” is online at http://www.nature.com/nature/journal/v480/n7375/full/nature10580.html.

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